Conventional golf balls can be divided into two general classes: solid and wound. Solid golf balls include one-piece, two-piece (i.e., single layer core and single layer cover), and multi-layer (i.e., solid core of one or more layers and/or a cover of one or more layers) golf balls. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by a tensioned elastomeric material, and a cover.
Examples of golf ball materials range from rubber materials, such as balata, styrene butadiene, polybutadiene, or polyisoprene, to thermoplastic or thermoset resins such as ionomers, polyolefins, polyamides, polyesters, polyurethanes, polyureas and/or polyurethane/polyurea hybrids, and blends thereof. Typically, outer layers are formed about the spherical outer surface of an innermost golf ball layer via compression molding, casting, or injection molding.
From the perspective of a golf ball manufacturer, it is desirable to have materials exhibiting a wide range of properties, such as resilience, durability, spin, and “feel,” because this enables the manufacturer to make and sell golf balls suited to differing levels of ability and/or preferences. In this regard, playing characteristics of golf balls, such as spin, feel, CoR and compression can be tailored by varying the properties of the golf ball materials and/or adding additional golf ball layers such as at least one intermediate layer disposed between the cover and the core. Intermediate layers can be of solid construction, and have also been formed of a tensioned elastomeric winding. The difference in play characteristics resulting from these different types of constructions can be quite significant.
Meanwhile, a golf ball's durability remains an important consideration. In this vein, the impact resistance of golf ball materials is an important property. Two important golf ball characteristics relating to impact resistance include elongation and compression set. Elongation is a measure of a material's elasticity and ability to withstand repeated blows on the course without fracturing. Compression set, meanwhile, is a measure of the material's ability to return to its original thickness after prolonged compressive stresses at a given temperature and deflection. Compression set results are typically expressed as a percentage, wherein a lower percentage indicates a better ability to resist permanent deformation.
On the one hand, golf ball materials having insufficient elongation are generally too brittle or stiff to remain in-tact when the golf ball is subjected to repeated blows by a club face at typically high swing speeds. On the other hand, permanent deformation of a golf ball layer material can create spaces or other separation between that layer and an adjacent layer which reduces golf ball durability.
Developing materials having balanced elongation and compression set can be difficult without meanwhile negatively impacting other desirable golf ball properties and increasing manufacturing costs. Accordingly, there is a continued need for cost effective golf ball constructions durably incorporating materials having both of these abilities to withstand the great force and impact of the golf club face striking the golf ball yet excellent “memory” or capacity to repeatedly return to its original shape following that great force and impact. Golf balls of the invention and methods of making same address and solve these needs.